Since fiber-forming, melt-spinnable, synthetic polymers were introduced, fiber manufacturers have looked for ways to increase the strength and stability properties of the fibers made from those polymers. The additional strength and stability properties of the fibers are needed so that applications beyond textile uses could be opened for their products. Such non-textile uses (also known as "industrial uses") include: tire cord; sewing thread; sail cloth; cloth, webs or mats used for road bed construction or other geo-textile applications; industrial belts; composite materials; architectural fabrics; reinforcement in hoses; laminated fabrics; ropes; and the like.
Originally, rayon was used in some of these industrial uses. Thereafter, nylon supplanted rayon as the material of choice. In the 1970's, conventional polyesters, such as polyethylene terephthalate, were introduced into competition against nylon. In about 1985, higher performance polyesters, i.e. higher strength and greater stability, were introduced.
A brief review of some of the patent prior art, summarized below, indicates that three general areas have been investigated as possible ways of enhancing the strength and stability properties of these synthetic fibers. Those general areas include processes directed to drawing; processes directed to the polymer; and processes directed to the spinning. Hereinafter, the term "drawing" shall refer to the heating and stretching performed on an as-spun yarn. The term "treatment to the polymer" shall refer to those things done to the polymer prior to spinning. The term "spinning" shall refer to processes for forming filaments from polymer, but excluding drawing.
The processes directed to drawing are as follows:
In U.S. Pat. No. 3,090,997, multistage drawing of polyamides, for use as tire cords, is disclosed. The fibers (nylon) are melt-spun in a conventional fashion. Thereafter, spun fibers are drawn in a three-stage process (drawn, then heated, then drawn again) to obtain a drawn nylon having the following properties: tenacity ranging from 10.4 to 11.1 grams per denier (gpd); elongation ranging from 12.9 to 17.1%; and initial modulus of 48 to 71 gpd/100%.
In U.S. Pat. No. 3,303,169, there is disclosed a single-stage drawing process for polyamides that yields high modulus, high tenacity, and low shrinkage polyamide yarns. The spun polyamide is drawn and heated to at least 115.degree. C. to obtain a yarn having: tenacity in the range of 5 to 8.7 gpd; elongation ranging from 16.2 to 30.3%; initial modulus of 28 to 59 gpd/100%; and shrinkage ranging from 3.5 to 15%.
In U.S. Pat. No. 3,966,867, a two-stage drawing process for polyethylene terephthalate having a relative viscosity of 1.5 to 1.7 is disclosed. In the first stage, the fibers are subjected to a temperature between 70.degree. and 100.degree. C. and a draw ratio of 3.8 to 4.2. In the second stage, the fibers are subjected to a temperature between 210.degree. and 250.degree. C. and a draw ratio, in the aggregate of the first draw ratio and second draw ratio, in the range of 5.6 to 6.1. The drawn yarn obtained has the following properties tenacity, 7.5 and 9.5 gpd; elongation, approximately 2 to 5% at a load of 5 gpd; elongation at break, 9 to 15%; and shrinkage, 1 to 4%.
In U.S. Pat. No. 4,003,974, polyethylene terephthalate spun yarn, having an HRV of 24 to 28, is heated to 75.degree. to 250.degree. C. while being drawn, is then passed over a heated draw roll, and finally relaxed. The drawn yarn has the following properties: tenacity, 7.5 to 9 gpd; shrinkage, about 4%; elongation at break, 12 to 20%; and load bearing capacity of 3 to 5 gpd at 7% elongation.
Those processes directed to enhancing yarn properties by treatment to the polymer are as follows:
In U.S. Pat. Nos. 4,690,866 and 4,867,963, the intrinsic viscosity (I.V.) of the polyethylene terephthalate is greater than 0.90. In U.S. Pat. No. 4,690,868, the as-spun (undrawn) fiber properties are as follows: elongation at break, 52 to 193%; birefriengence, 0.0626 to 0.136; and degree of crystallinity, 19.3 to 36.8%. The drawn fiber properties are as follows: tenacity, 5.9 to 8.3 gpd; elongation, 10.1 to 24.4%; and dry shrinkage (at 210.degree. C.), 0.5 to 10.3%. In U.S. Pat. No. 4,867,936, the drawn fiber properties are follows: tenacity, about 8.5 gpd; elongation at break, about 9.9%; and shrinkage (at 177.degree. C.), about 5.7%.
Those processes directed to spinning are as follows:
In U.S. Pat. No. 3,053,611, polyethylene terephthalate after leaving the spinneret is heated to 220.degree. C. in a spinning shaft two meters long. Thereafter, cold water is sprayed onto the fibers in a second shaft. The fibers are taken up at a speed of 1,600 meters per minute (mpm) and are subsequently drawn to obtain a tenacity of 3.5 gpd.
In U.S. Pat. No. 3,291,880, a polyamide is spun from a spinneret and then cooled to about 15.degree. C., then the fiber is sprayed with live steam. The as-spun fiber has a low orientation and a low birefriengence.
In U.S. Pat. No. 3,361,859, a synthetic organic polymer is spun into a fiber. As the fibers exit the spinneret, they are subjected to "controlled retarded cooling". This cooling is conducted over the first seven inches from the spinneret. At the top (i.e. adjacent the spinneret), the temperature is 300.degree. C. and at the bottom (i.e. approximately 7 inches from the spinneret), the minimum temperature is 132.degree. C. The as-spun yarn has a low birefriengence (11 to 35.times.10.sup.-3) and drawn yarn properties are as follows: tenacity, 6.9 to 9.4 gpd; initial modulus, 107 to 140 gpd/100%; and elongation at break, 7.7 to 9.9%.
In U.S. Pat. Nos. 3,936,253 and 3,969,462, there is disclosed the use of a heated shroud (ranging in length from one-half foot to two feet) with temperatures ranging from about 115.degree. to 460.degree. C. In the former, the temperature is greater at the top of the shroud than at the bottom. The drawn yarn properties of the former are as follows: tenacity, 9.25 gpd; elongation, about 13.5%; and shrinkage, about 9.5%. In the latter, the temperature is constant within the shroud and the drawn yarn properties are as follows: tenacity, 8 to 11 gpd; and elongation at break, 12.5 to 13.2%.
In U.S. Pat. No. 3,946,100, fibers are spun from a spinneret and solidified at a temperature below 80.degree. C. The solidified fibers are then reheated to a temperature between the polymer's glass transition temperature (Tg) and its melting temperature. This heated fiber is withdrawn from the heating zone at a rate of between 1,000 to 6,000 meters per minute. Spun yarn properties are as follows: tenacity, 3.7 to 4.0 gpd; initial modulus, 70 to 76 gpd/100%; and birefriengence, 0.1188 to 0.1240.
In U.S. Pat. No. 4,491,657, polyester multifilament yarn is melt-spun at high speed and solidified. Solidification occurs in a zone comprising, in series, a heating zone and a cooling zone. The heating zone is a barrel shaped heater (temperature ranging from the polymer's melting temperature to 400.degree. C.) ranging in length from 0.2 to 1.0 meters. The cooling zone is cooled by air at 10.degree. to 40.degree. C. Drawn yarn made by this process has the following properties: initial modulus, 90-130 gpd; and shrinkage (at 150.degree. C.) less than 8.7%.
In U.S. Pat. No. 4,702,871, fiber is spun into a chamber having a subatmospheric pressure. Spun yarn properties are as follows: strength, 3.7 to 4.4 gpd; birefriengence, 104.4 to 125.8 (.times.10.sup.-3); and dry heat contraction, 4.2 to 5.9% at 160.degree. C. for 15 minutes.
In U.S. Pat. No. 4,869,958, the fiber is spun in the absence of heat and then taken up. At this point, the fiber has a low degree of crystallinity, but it is highly oriented. Thereafter, the fiber is heat treated. The drawn fiber properties are as follows: tenacity, 4.9 to 5.2 gpd; initial modulus, 92.5 to 96.6 gpd/100%; and elongation, 28.5 to 32.5%.
The foregoing review of patents indicates that while some of the fibers produced by these various processes have high strength or low shrinkage properties, none of the foregoing patents teach of a yarn or a process for producing such a drawn yarn having the combination of high tenacity, high initial modulus, and low shrinkage.
The patents which come closest to teaching such a drawn yarn are U.S. Pat. Nos. 4,101,525 and 4,195,052, related patents that are assigned to the assignee of the instant invention. In these patents, the polyester filaments (the polymer having an intrinsic viscosity of 0.5 to 2.0 deciliters per gram) are melt spun from a spinneret. Molten filaments are passed through a solidification zone where they are uniformly quenched and transformed into solid fibers. The solid fibers are drawn from the solidification zone under a substantial stress (0.015 to 0.15 gpd). These as-spun solid fibers exhibit a relatively high birefriengence (about 9 to 70.times.10.sup.-3). The as-spun fibers are then drawn and subsequently heat treated. The drawn filament properties are as follows: tenacity, 7.5 to 10 gpd; initial modulus, 110 to 150 gpd/100%; and shrinkage, less than 8.5% in air at 175.degree. C.